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Subject: Re: [OMPI devel] RGET issue when send is less than receive
From: George Bosilca (bosilca_at_[hidden])
Date: 2013-06-21 11:52:28


The amount of bytes received is atomically updated on the completion callback, and the completion test is clearly spelled-out int the recv_request_pml_complete_check function (of course minus the lock part). Rolf I think your patch is correct.

That being said req_bytes_expected is a special value, one that should only be used to check from truncation. Otherwise, req_bytes_packed is the value we should compare against.

  George.

On Jun 21, 2013, at 17:40 , Nathan Hjelm <hjelmn_at_[hidden]> wrote:

> I thought I fixed this problem awhile back (though looking at the code its possible I never committed the fix). I will have to look through my local repository and see what happened to that fix. Your fix might not work correctly since a RGET can be broken up into multiple get operations. It may work, I would just need to test it to make sure.
>
> -Nathan
>
> On Fri, Jun 21, 2013 at 08:25:29AM -0700, Rolf vandeVaart wrote:
>> I ran into a hang in a test in which the sender sends less data than the receiver is expecting. For example, the following shows the receiver expecting twice what the sender is sending.
>>
>> Rank 0: MPI_Send(buf, BUFSIZE, MPI_INT, 1, 99, MPI_COMM_WORLD)
>> Rank 1: MPI_Recv(buf, BUFSIZE*2, MPI_INT, 0, 99, MPI_COMM_WORLD)
>>
>> This is also reproducible using one of the intel tests and adjusting the eager value for the openib BTL.
>>
>> ? mpirun -np 2 -host frick,frack -mca btl_openib_eager_limit 56 MPI_Send_overtake_c
>>
>> In most cases, this works just fine. However, when the PML protocol used is the RGET protocol, the test hangs. Below is a proposed fix for this issue.
>> I believe we want to be checking against req_bytes_packed rather than req_bytes_expected as req_bytes_expected is what the user originally told us.
>> Otherwise, with the current code, we never send a FIN message back to the sender.
>>
>> Any thoughts?
>>
>> [rvandevaart_at_sm065 ompi-trunk]$ svn diff ompi/mca/pml/ob1/pml_ob1_recvreq.c
>> Index: ompi/mca/pml/ob1/pml_ob1_recvreq.c
>> ===================================================================
>> --- ompi/mca/pml/ob1/pml_ob1_recvreq.c (revision 28633)
>> +++ ompi/mca/pml/ob1/pml_ob1_recvreq.c (working copy)
>> @@ -335,7 +335,7 @@
>> /* is receive request complete */
>> OPAL_THREAD_ADD_SIZE_T(&recvreq->req_bytes_received, frag->rdma_length);
>> - if (recvreq->req_bytes_expected <= recvreq->req_bytes_received) {
>> + if (recvreq->req_recv.req_bytes_packed <= recvreq->req_bytes_received) {
>> mca_pml_ob1_send_fin(recvreq->req_recv.req_base.req_proc,
>> bml_btl,
>> frag->rdma_hdr.hdr_rget.hdr_des,
>>
>>
>>
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